1. Field of the Invention
The present invention generally relates to exhaust control valves for an engine. More specifically, the present invention relates to an exhaust control valve control arrangement that provides an exhaust valve cleaning mode which reduces the likelihood of such valves sticking as a result of use.
2. Description of Related Art
Conventional two-stroke engines generally include an exhaust port provided in each cylinder wall such that spent gases are exhausted through the exhaust port as the piston reciprocates in the cylinder. Exhaust port timing has an important effect on engine performance. Optimum exhaust port timing is dependent, in part, upon engine speed. For instance, to provide an improved engine performance, the exhaust port timing can be advanced during high-speed engine operation relative to the exhaust port timing during engine idling.
One manner of controlling the exhaust port timing is to employ exhaust control valves. Generally, these valves are of the sliding or rotating type, and do not serve to ever completely close the opening or port in each combustion chamber in two-stroke applications. Instead, each valve moves between a first position, in which the valve does not obstruct, or obstructs very little of, the exhaust port, and a second position, in which the valve partially obstructs the port. Therefore, the exhaust control valve can alter the effective cross-sectional area of the exhaust port by appearing to lower an upper surface of the exhaust port, thereby restricting the flow through the exhaust port. The movement of the valves also alters the timing of the opening and closing of the exhaust ports.
By extending the exhaust control valve into the exhaust port, it is possible to operate the engine under a higher compression ratio under low-load and low-speed conditions to improve engine performance. It is also possible to reduce the compression ratio under high-speed and high-load conditions by retracting the exhaust control valve to avoid excess pressures in the combustion chamber and pre-ignition or knocking conditions. Furthermore, closing the exhaust control valve during starting can raise the compression ratio and facilitate starting. Hence, these types of exhaust control valves are extremely effective in improving the performance of a two-stroke engine under particularly difficult running conditions without sacrificing performance under other running conditions.
There is a difficulty in conjunction with these valves however. Because the exhaust control valve is subject to exhaust gas temperatures, there must be adequate clearance provided between the valve and its surrounding structure to permit the valve to slide or rotate freely between its opened and closed positions. Of course, this clearance cannot be so great as to cause pressure leakage. In addition, because of the different materials typically employed for the exhaust control valve and the engine casting, in which the valve is mounted, compensation for differing degrees of thermal expansion is necessary. Accordingly, the clearances may actually be less when the engine is cold than when it is warm. Therefore, when the engine is started, before the engine is warmed-up, the valves are more prone to sticking.
Moreover, because these valves have a relatively small range of movement, and are not continuously moved, they may seize within the guide passage in which they are mounted. In addition, because oil may be present in the exhaust gases of two cycle engines, the oil can cause a further problem once the engine is shut off. While the engine is running, the temperature will be high enough to avoid carbonization on the valve. However, as a stopped engine cools, residual oil may carbonize, or coke, on the control valve and form deposits. These deposits, along with other foreign matter, such as sea-salt for instance, make it difficult to operate the valve when the engine is restarted. In short, these deposits tend to inhibit a smooth operation of the valve. Of course, the aforementioned differential thermal expansions will also further aggravate this situation.
It has been suggested to exercise the exhaust control valves through a number of cycles between an opened and a closed position to clean any scale, carbon deposits or other debris from the exhaust control valve. However, the cycling of the exhaust control valve presents problems in and of itself. For instance, if the exhaust control valve is being cycled through a large range of movement while the engine is under acceleration, the effective compression ratio of the engine is also being altered throughout the movement of the valve and during the acceleration of the watercraft. This can result in uneven acceleration as well as an uncomfortable ride.
Thus, an exhaust control valve control arrangement is desired that can be used in an engine for powering a watercraft. The control should be reliable and easy to maintain. Moreover, it is desired to have a cleaning operation for exhaust control valves, which does not significantly detract from the performance characteristics of the watercraft engine during rapid acceleration.
In accordance with one feature of the present invention, the exhaust control valve prioritizes engine acceleration over exhaust valve cleaning. For instance, the cleaning is performed during start-up and shutdown but not while the watercraft rapidly accelerates to attain a planing velocity. In addition, if the throttle is suddenly fully opened, then any cleaning operation in progress at that time is ceased.
Another feature of the present invention provides an improved exhaust control valve system and method of operating the same. Additionally, an exhaust control valve system configured in accordance with the present invention desirably provides a method for cleaning an exhaust control valve under at least some conditions that may reduce the possibility of valve sticking on start up and during low-temperature operation. Moreover, the exhaust control valve system preferably prioritizes the acceleration of the engine over the cleaning operation.
Accordingly, one aspect of the present invention involves a watercraft having an engine powering a water propulsion unit. The engine includes a starter motor, an exhaust port leading from a combustion chamber through which the exhaust products may be transported and an exhaust valve cooperable with the exhaust port. The exhaust valve is movable between a first position, in which the closing of the exhaust port is delayed, and a second position, in which the closing of the exhaust port is advanced. The watercraft also has a control unit powered by a power source and a drive control for moving the exhaust valve at least partially between the first position and the second position in an exhaust cleaning operation. The control unit activates the drive control after the starter motor is engaged and before the engine attains a first predetermined speed so as to cycle the exhaust control valve. The control unit deactivates the drive control after the engine attains a second predetermined speed so as to disable controlled movement of the exhaust control valve.
Another aspect of the present invention involves a watercraft having an engine powering a water propulsion unit. The engine includes a starter motor and an exhaust port leading from a combustion chamber through which the exhaust products may be transported. The engine also has an exhaust valve cooperable with the exhaust port which is movable between a first position, in which the closing of the exhaust port is delayed, and a second position, in which the closing of the exhaust port is advanced. The watercraft also has a control unit which is in electrical communication with a drive control. The drive control is capable of moving the exhaust valve at least partially between the first position and the second position in an exhaust cleaning operation. The control unit desirably activates the drive control before the engine attains a first predetermined speed so as to cycle the exhaust control valve.
An additional aspect of the present invention involves an exhaust control for an exhaust valve of an internal combustion engine. The engine includes at least one combustion chamber and an intake passage leading to the combustion chamber for providing air thereto. The engine also has a fuel supply for supplying fuel to the combustion chamber and an exhaust port leading from the combustion chamber for routing exhaust products therefrom. The valve desirably cooperates with the exhaust port and is movable between a first position, in which the closing of the exhaust port is delayed, and a second position, in which the closing of the exhaust port is advanced. The exhaust control includes means for moving the valve between the first and second positions and control means for moving the valve in a cleaning operation at least partially between the first and second positions when the engine is running at a speed below a predetermined speed.
A further aspect of the present invention involves an engine having at least one combustion chamber with an exhaust port leading therefrom. An exhaust port timing control valve is provided in the port at an upper portion thereof. Desirably, the valve can be moved between a projected position wherein it is projected into the exhaust port and covers at least the upper portion of the exhaust port and a retracted position in which it is retracted from the exhaust port. A drive control is provided that is capable of moving the valve and a main control is also provided that is capable of controlling the drive control between on and off states. The main control operates the drive control in a cleaning mode and a regular valve operation mode and the control unit initiates a valve cleaning mode in which the valve is moved between its projected and retracted positions by the drive control when a speed of the engine after starting exceeds a predetermined low speed but is below a predetermined high speed.
Another aspect of the present invention involves a method of cleaning an exhaust control valve of an engine. The engine has a lanyard switch, a start switch and at least one combustion chamber. An exhaust passage leads from the chamber. The exhaust control valve cooperates with the passage. The method involve determining if the lanyard switch is in an on position and determining if the start switch is in the on position. Once both of these switches are in an on position, the method determines if the engine speed exceeds a first predetermined speed. If so, the valve is moved in a cleaning operation between at least partially between a first position in which the valve does not obstruct the passage and a second position in which the valve at least partially obstructs the passage in order to clean the valve.